Interpretive Summary: Stripe rust is one of the most important diseases of wheat worldwide. The disease is best controlled by growing resistant cultivars. Understanding molecular mechanisms of resistance to stripe rust may lead to more effective strategies to control the disease. We used the microarray technology to study the race-specific resistance controlled by Yr5, a wheat gene conferring all-stage resistance to all races of the wheat stripe rust pathogen identified so far in the United States. Through time-course experiments, we identified numerous plant-defense related genes that are important for major resistance gene-mediated resistance as well as basal defense in wheat. From the expression changes of identified genes in the rust infection time course, we derived a model that links the fungal pathogen recognition to the expression of plant defense responses. The presence of the Yr5 resistance gene resulted in a rapid and amplified resistance response involving signaling pathways and defense-related transcripts known to occur during resistance gene-mediated responses. Basal defense also involved substantial induction of many defense-related transcripts but the lack of resistance gene signaling resulted in a delayed and weaker response, most likely due to the absence of increased cellular signaling and nitric oxide production that were able to confer an effective resistance response in the presence of Yr5. The data generated provides novel insights into the cellular and molecular mechanisms of wheat defense to an economically important pathogen, and the findings will be useful for the development of durable resistant cultivars.

Technical Abstract:
The Wheat GeneChip® was used to profile the changes occurring in two wheat isolines that differed for the presence of the Yr5 gene after inoculation with the stripe rust pathogen Puccinia striiformis Westend. f. sp. tritici Eriks. Yr5 represents a single R gene that confers all-stage resistance to all currently known North American races of P. s. tritici. This time-course study identified numerous defense-related transcripts that were important for R-gene-mediated race-specific resistance as well as basal defense, and supported a model that links P. s. tritici recognition to the expression of plant defense responses. The presence of Yr5 resulted in a rapid and amplified resistance response involving signaling pathways and defense-related transcripts known to occur during R¬-gene-mediated responses. Basal defense also involved substantial induction of many defense-related transcripts but the lack of R-gene signaling resulted in a delayed and weaker response, most likely due to the absence of increased cellular signaling and nitric oxide production that were able to confer an effective hypersensitive response in the presence of Yr5. The data generated provides novel insights into the cellular mechanisms of wheat defense to an economically important pathogen, and the findings will be useful for the development of durable resistant cultivars.